1. Field of the Invention
The invention relates in general to a multi-broad band antenna and a portable electronic device thereof, and more particularly to a multi-broad band antenna resonating many broad bands with a single conductive structure and a portable electronic device thereof.
2. Description of the Related Art
Normally, an antenna resolves the multi-path interference problem by an antenna diversity structure. When a radio frequency system adopts multi-band operation, most antennas achieve antenna diversity by many independent antennas or a composite antenna. As a result, the system becomes complicated and the operating reliability is reduced. Thus, conventional multi-band antenna excites many resonant modes according to the frequency-doubling effect of resonant structure to achieve multi-band operation.
However, the above design is subjected to the restriction that the central frequencies of the resonant modes form a multiple relationship and that all bandwidths of the resonanat modes are narrow bands such that the bandwidth of the antenna is difficult to expand. For example, the 2.4 GHz and 5 GHz dual-band antenna used in a wireless local area network (WLAN) normally receives and transmits a 5 GHz electromagnetic wave signal by adjusting the structural parameters of 2.4 GHz double-band resonant mode (that is, 4.8 GHz). Thus, the efficiency in the transmission of high frequency electromagnetic wave is normally poor, largely affecting signal quality. Furthermore, as the multiple relationships among the resonant modes, the frequency-doubling effect is not applicable to the frequency ranges of 2.4˜2.4835 GHz, 4.9˜5.35 GHz, 5.47˜5.725 GHz and 5.725˜5.825 GHz required for the operation of WLAN 802.11a/b/g. This is because the multiple relationship does not exist in the bands of 5 GHz frequency range, and the overall bandwidth is too wide (approximates 1 GHz).
Current trends of notebook computer are focused on diversified wireless communication functions, particularly the ultra mobile PC (UMPC) further incorporates global positioning system (GPS). Thus, to incorporate the global standard for mobile system (GSM) within 824˜894 MHz and 1850˜1990 MHz, the global positioning system within 1.575 GHz and the WLAN system within 2.4˜2.5 GHz and 4.9˜5.875 GHz in a single structure is a great challenge to the volumetric efficiency of an antenna and the electrical characteristics thereof.